Chemical Signatures Associated with the Freshening of Northern 
Atlantic Waters between 1972 and 1981 
Wallace S. Broecker 
Lamont-Doherty Geological Observatory 
Palisades, New York 10964 
Further insight into the possible causes of the freshening of deep water in the northern 
Atlantic between the GEOSECS survey (1972) and the TTO survey (1981) is provided by measure- 
ments of dissolved silica and dissolved oxygen. As all the northern end member waters are low 
in dissolved silica content and high in dissolved oxygen content, the message carried by these 
chemical properties of silica has to do with the extent to which the waters in the northern 
Atlantic have mixed with the high silica content waters of Antarctic origin. A change in the 
degree and pattern of this intrusion is noted between the GEOSECS and TTO surveys. 
On the map in Figure 1 the locations of GEOSECS stations 8, 5, 4, 2, 27 and 24 are 
superimposed on the TTO track map. In Figure 2 through 7 comparisons are made of the sali- 
nity, initial phosphate (PO4°), dissolved silica (H4SiO4) and apparent oxygen utilization (AOU) 
values for these GEOSECS stations and the nearest TTO stations. In each case potential tem- 
perature serves as the reference parameter. 
c Lorge Volume 
Transient 6 Small Volume 
Tracers in the 
Ocean 
1981 
80W 60W ~~ 40W 20W 
Fig. 1. Locations of GEOSECS stations 8, 5, 4, 2, 27 and 24 superimposed on the TTO track. 
